Аннотация:Abstract. Important problems of magma differentiation, the formation of native metals and ore formation processes in the earth's crust, are increasingly associated with the active participation of hydrogen. In this
paper, new experimental data on the crystallization of basalt melts at high temperatures (1100-1250 oC) and hydrogen pressures (10-100 MPa) are obtained, which clarify the possible role of hydrogen in processes occurring in basalt melts in the earth's crust and during volcanism under highly reducing conditions (f(O2) = 10 -14). In crystallization experiments, it was found that the compositions of crystals (olivines, clinopyroxenes and plagioclases) formed in the experiment on the crystallization of a melt of magnesium basalt under hydrogen pressure closely correspond to the compositions of crystals of lava flows of the Northern breakout
of Tolbachik volcano in Kamchatka. This result can be considered as an experimental confirmation of the participation of hydrogen in the volcanic process.